Essentially you are right, but the snapshot commit process is asynchronous. That's what you have to pay for exactly once semantics.
Li Wang <wangli1...@gmail.com>于2016年11月1日周二 下午3:05写道： > Hi all, > > I have a question regarding to the state checkpoint mechanism in Flink. I > find the statement "Once the last stream has received barrier n, the > operator emits all pending outgoing records, and then emits > snapshot n barriers itself” on the document > https://ci.apache.org/projects/flink/flink-docs-master/internals/stream_checkpointing.html#exactly-once-vs-at-least-once > . > > Does this mean that to achieve exactly-once semantic, instead of sending > tuples downstream immediately the operator buffers its outgoing tuples in a > pending queue until the current snapshot is committed? If yes, will this > introduce significant processing delay? > > Thanks, > Li > > -- Liu, Renjie Software Engineer, MVAD
